Furnace muffle

ABSTRACT

A FURNACE MUFFLE OF UNIQUE WELDED CONSTRUCTION AND ESPECIALLY ADAPTED FOR OPERATION AT EXTREME OPERATING TEMPERATURES. THE MUFFLE IS FORMED AS AN ELONGATED TUBULAR MEMBER HAVING ONE OR MORE GAS PIPES INTEGRALLY FORMED THEREIN TO INTRODUCE A GASEOUS ATMOSPHERE WITHIN THE MUFFLE. THE ENTIRE MUFFLE STRUCTURE INCLUDING THE GAS PIPES IS FORMED OF A METAL WHICH HAS EXPERIENCED THE SAME WORK HISTORY DURING FABRICATION, AND INDIVIDUAL ELEMENTS OF THE MUFFLE STRUCTURE ARE WELDED IN A UNIQUE MANNER TO PROVIDE A UNITARY STRUCTURE ARE WELDED IN A UNIQUE MANNER TO PROVIDE TION AT ELEVATED TEMPERATURES.

Oct. 26, 1971 J. H. BECK 3,615,082

' FURNACE MUFFLE Filed Sept. 2, 1969 Fig. 4.

JACOB HOWARD BECK INVIN'l'( )R United States Patent Olhce 3,6I5,082Patented Oct. 26, 1971 3,615,082 FURNACE MUFFLE Jacob Howard Beck,Waban, Mass., assignor to BTU Engineering Corporation, Waltham, Mass.Filed Sept. 2, 1969, Ser. No. 854,648 Int. Cl. F27b 5 04 U.S. Cl. 263-415 Claims ABSTRACT OF THE DISCLOSURE A furnace muiiie of unique weldedconstruction and especially adapted for operation at extreme operatingtemperatures. The muflie is formed as an elongated tubular member havingone or more gas pipes integrally formed therein to introduce a gaseousatmosphere within the muffle. The entire mui'lie structure including thegas pipes is formed of a metal which has experienced the same workhistory during fabrication, and individual elements of the mutiiestructure are welded in a unique manner to provide a unitary muiileconstruction capable of superior operation at elevated temperatures.

FIELD OF THE INVENTION This invention relates to furnace muiiies andmore particularly to a welded muflie construction capable of providingsuperior operation at extreme elevated temperatures.

BACKGROUND OF THE INVENTION Moving conveyor mufiie furnaces are widelyemployed in the heat processing of components and devices such as thicklilm circuits. The furnace muffle is formed as an elongated tubularmember having a bottom wall which serves as a hearth for support of amoving conveyor thereon for transport of the work load through thefurnace. The muflie may be divided into zones, each of which can beindividually controlled to maintain separate temperatures and each ofwhich may contain a different gaseous environment according to theparticular heat processing being performed. In order to maintain uniformtemperature within the muie and in order to provide a sealed gaseousatmosphere, the mufe is formed as a closed tu'bular member and it isimportant that the integrity of the mufiie structure be maintained overa wide range of operating temperatures without distortion in order notto detract from proper furnace operation.

The gaseous environment within the mufe is often provided by one or moregas pipes disposed along the length of the mutile and welded to theinterior mui-lle wall. Such gas pipes, however, usually have differentmetallurgical characteristics and work history than the metal formingthe muie. As a result, the gas pipe has different thermal expansioncharacteristics than that of the mul'lie, as a consequence of which thepipe can physically distort during furnace operation. In an attempt toavoid such distortion, conventional furnace mutiles have beenconstructed in which the gas pipe is supported within the muffle bymeans of brackets attached to the mufe wall. This latter approach, whilelessening the problem of distortion to some extent, suffers thedisadvantage of additional support structures within the mutlie, whichadd to the cost of muffle fabrication, as well as giving rise topossible sources of contamination with the mufie at elevatedtemperatures.

SUMMARY OF THE INVENTION In accordance with the present invention afurnace muffle of improved construction is provided which is especiallyadapted for superior operation at elevated temperatures. All elements ofthe muie structure are formed of metal having identical metallurgicalcharacteristics and having the same cold and hot metal working history,such that a mulfle so constructed exhibits uniform thermal expansion andstress relieving over the operating temperature range. Typically, themuie is formed of first and second elongated metal members of generallyU-shaped cross section, arranged to -be welded along their confrontingedges to provide a closed tubular muiiie structure. The confrontingedges of the mufe sections are of predetermined beveled configurationand a gas pipe formed from a metal having the same work history as thesections of the mufe is disposed between the beveled confronting edgesof the mufiie sections. A portion of the gas pipes serves as a source ofwelding material and permits a mechanically strong unitary mutiie to beprovided capable of operation at extreme elevated temperatures withoutdistortion.

DESCRIPTION OF THE DRAWINGS The invention will be more fully understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. l is a cutaway pictorial View of a furnace mufie constructedaccording to the invention;

FIG. 2 is an elevation view, partly in section, of the unique mutlieconstruction prior to welding;

FIG, 3 is an elevation view, partly in section, of the muflle structureafter welding; and

FIG. 4 is a cutaway pictorial view of an alternative ernbodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION A furnace muliie of unique unitaryconstruction and adapted for superior operation at elevated temperaturesis illustrated in FIG. l. The muflie 10 is of elongated tubularconfiguration and includes a first muflie section 12 of generallychannel-shaped cross section intimately joined to a second mutliesection 14 of generally U-shaped configuration. First and second gaspipes 16 and 18 are respectively joined to muflie sections 12 and 14 attheir respective junctures. Gas pipes 16 and 18 each extend along thelength of a respective side wall of muflie 10 and include a plurality ofopenings 20 therein spaced along the length of the gas pipes to transmitgas introduced within pipes 16 and 18 into the interior of the muliie10. A predetermined gaseous environment can thus be maintained withinthe interior of the muie.

Muffle section 12 includes a bottom wall 22 which serves as a hearth forthe support of a movable conveyor belt 24 thereon. Conveyor belt 24 istypically formed of woven wire or chain link construction and istransported through the interior of muflie 10 by a suitable transportmechanism (not shown). A work load is thereby transportable through themuiie by means of moving conveyor 24. Muflie section 12 also includesside walls 13 and 15 formed at right angles to bottom wall 22 and joinedto section 14 and respective gas pipes 16 and 18 by the uniquecontinuous welds 17. The muflie section 14 is of a smoothly curvedconfiguration and provides the arched roof of muflie 10.

The muie elements described hereinabove are continuously and uniquelywelded to provide the unitary mufiie structure illustrated in FIG. 1having a continuous weld 17 along each side wall thereof. The weld 17 isof large area and has substantially the same characteristics as thematerial forming the muie elements. As a result, a muie formed accordingto the invention, in a manner to be described, is operative over a widetemperature range and exhibits uniform stress relief and thermalexpansion characteristics and maintains structural integrity even atextreme operating temperatures. It is a particular feature of theinvention that all elements of the muiie are formed of metal which hasexperienced the same cold and hot Work history su'ch that the entireunitary mutiie structure exhibits the same thermal expansioncharacteristics and experiences substantially uniform stress relief overan operating temperature range. The muiie is formed of a hightemperature alloy such as Inconel, the metal preferably being crossrolled to provide impro-ved stress-relieved characteristics. Gas pipes16 and 18 are formed in a configuration operative to assist in theachievement of a mechanically strong weld between the muie sections 12and 14 and gas pipe contained therebetween.

The confronting edges of muliie sections 12 and 14 and the portion ofrespective gas pipes 16 and 18 disposed therebetween and intimatelybonded thereto are adapted according to the invention to provide asuperior weld as a result of which a unique unitary mufiie structure isprovided which is capable of operation and which maintains itsstructural integrity over a Wide range of operating temperatures.

Construction of the unitary muliie structure is accomplished by a uniquewelding technique which provides an extremely strong large area weldbetween the elements of the muiie being fabricated. Referring to FIG. 2,there is shown the confronting edges of mutlie sections 12 and 14 withgas pipe 16 disposed therebetween, prior to welding of these elementsinto a unitary structure. Gas pipe 18 is identically fabricated on theother side wall of mufie 10. A bevel 40 is formed on the upper edge ofse'ction 12 and a similar bevel 42 is formed on the edge of mufliesection 14. The bevels extend across approximately half the Iwallthickness of respective muiiie sections 12 and 14 and are formed on theside of the muflie sections opposite to the location of gas pipe 16.

The confronting edges of muie sections 12 and 14 also includenon-beveled portions 41 and 43 which extend across the other half of thewall thickness of the muiiie sections and are formed substantiallyorthogonal to the plane of the mule side walls on which they aredisposed. A V-shaped region is defined by the confronting beveled edgesalong the length of muflie sections 12 and 14 and this region iseffective to permit the formation of a deep large area weld, which, inaccordance with the invention, provides the improved unitary mufflestructure.

As discussed hereinabove, the gas pipes 16 and 18 are formed into thedesired shape from a metal having the same work history as the metalemployed to fabricate sections 12 and '14 of the furnace muiiie. Asillustrated in FIG. 2, gas pipe 16 includes a tubular portion 44, and aange portion 46 which is disposed between the confronting non-bevelededges 41 and 43 of respectice muiiie sections 12 and 14. The angeportion 46 extends into the V-shaped region defined by the beveled edges`40 and 42 and may extend beyond the plane of the substantially coplanarwalls of muiiie sections 12 and 14.

As a particular feature of the invention, the flange portion 46 of thegas pipes serves as a source of material for forming the unitary weldedmuiiie structure. This ange portion is of the same metal and has thesame Work history as muie sections 12 and 14, and the weld formedaccording to the invention has essentially the same metallurgicalcharacteristics as the elements forming the muiiie. A mule thusconstructed is capable of operation at extreme elevated temperatureswithout degradation or distortion of the weldments.

The confronting surfaces of muflie sections 12 and 14 and the associatedgas pipe are continuously Welded along the length of the muie typilly byHeliarc welding to form the welded structure depicted in FIG. 3. Asdiscussed hereinabove, the metal of flange portion 46 serves as a sourceof welding material which flows into the V- shaped region dened by thebevel edges 40 and 42 of mu'lie sections 12 and 14, such that arelatively deep and large area weld of high physical strength isprovided. The surfaces 41 and 43 are also welded to the confrontingportions of flange portion 56. The boundary of the weld is depicted inFIG. `3 by the dotted generally hemispherical line 48. The metalemployed in muiiie sections 12 and A14 and the associated gas pipe isidentical and has the same work history, and exhibits substantiallyuniform stress relieving as temperature varies. The gas pipes andassociated muflie sections expand and contract by the same amount withtemperature variation and the welds have less tendency to deteriorateunder temperature cycling which may be experienced in operation and athigh elevated temperatures at which the furnace employing the muffleoperates. The muie constructed according to the invention thereformaintains its structural integrity even at extreme operatingtemperatures, with the result that reliable and controllable furnaceoperation is maintained.

An alternative embodiment of a muffle constructed according to theinvention is illustrated in FIG. 4 and includes an elongated tubularstructure 50 having an arched roof 52 and a substantially flat coplanarbottom. wall 54 which serves as the muiiie hearth for support of amovable conveyer belt 56 thereon. A generally V-shaped slot 5S is formedin bottom wall 54 of the muflie and extends longitudinally along thelength thereof. A gas pipe 60, formed of a metal having the samemetallurgical characteristics and work history as the metal forming themuiiie itself is disposed within the V-shaped slot 58 and is welded, inaccordance with the invention, to the lowermost confronting edges of theslot tol provide the superior unitary muflie structure. The uppermostsurface of gas pipe 60 lies substantially within or below the plane ofthe mufe hearth and does not interfere with movement of conveyer belt 56through the muffle. With the gas pipe 60 disposed below conveyer 56, themufe is free of protuberances, and gas pipe `60 is protected vagainstdamage and undue wear. The gas provides, via

openings 62 provided along the length thereof, a fresh supply of gaseousatmosphere which is directed up through the conveyer belt and whichiiows past the work product carried by the conveyer. As the gas isheated, it rises to the roof of the muflie away from the work productand can exit at the ends of the furnace.

lIn the embodiment of PEG. 4, the unitary muffle structure is formedwith a single weld between the confronting edges of the mufe wall inV-shaped slot 58 and the associated gas pipe 60. As describedhereinabove, continuous welding is employed to form a large areaextremely strong weld. It will be appreciated that, prior to Welding,the confronting edges of the inclined walls 64 and 66, deiine a V-shapedregion in which is disposed the ange portion of gas pipe 60. A bevelneed not be formed on the confronting edges of the muiiie wall in thisinstance since such a bevel is eifectively provided by the inclineddisposition of the confronting muffle walls. As described hereinabove,the gas pipe 60 and the muiiie 50 are of a metal having the samemetallurgical characteristics and work history, and the large area deepweld formed according to the invention provides a unitary mufflestructure capable of operation at extreme elevated temperatures withoutdegradation or distortion.

What is claimed is:

1. A furnace muflie comprising:

a first elongated member of generally U-shaped crosssection having firstand second elongated parallel edges of predetermined beveledconfiguration adapted to provide a mechanically strong large area Weld;

a second elongated member of generally U-shaped cross-section havingiirst and second elongated parallel edges of the same predeterminedbeveled configuration, the first and second edges of said second memberconfronting the first and second edges of said iirst member to form latubular muffle structure, the beveled edges of said confronting membersdefining a groove in each outer side wall of said confronting members;

first and second gas pipes, each having a tubular portion and anoutwardly extending flange portion, and each disposed on respectiveopposite sides of said muie structure with said tubular portion withinsaid confronting members and with said flange portion between and inintimate contact with said confronting edges and disposed in saidgroove;

said flange portion and confronting edges being continuously weldedalong the length thereof, said flange portion serving as a source ofwelding metal to provide -a mechanically strong large area weld in theregion of said predetermined beveled configuration and along the lengthof said mnie structure; and said irst and second elongated members andfirst and second gas pipes each being formed of an identical i metalhaving the same metallurgical characteristics and Work history such thatsaid members and gas pipes exhibit substantially uniform thermalexpansion and stress relieving.

2. A furnace muiiie according to claim 1 wherein said first and secondmembers each include a bevel found on the outer elongated parallel edgesthereof, the bevels of the confronting members defining a V-shapedgroove in the outer side Wall of said confronting members, and said angeportion being disposed in said V-shaped groove.

3. A furnace muie according to claim 1 wherein said predeterminedbeveled configuration includes a beveled portion formed acrossapproximately half the wall thickness of its elongated member, and anon-beveled portion formed across the other half of the wall thicknessof said member in a direction orthogonal to the plane of the mufflewall, the bevels of said confronting members defining a V-shaped groovein the outer side wall of said confronting members, and said angeportion being disposed in said V-shaped groove.

4. A furnace muiiie comprising:

an elongated member of closed cross-sectional configuration having firstand second confronting elongated parallel edges of predetermined beveledconfiguration defining a V-shaped groove in the outer wall of saidmember and adapted to provide a mechani- 40 cally strong large areaweld; a gas pipe having a tubular portion and an outwardly extendingange portion disposed with said tubular portion within said closedconguration and with said ange portion within said V-shaped groovebetween and in intimate contact with said confronting edges;

said elongated member and gas pipe each being formed of an identicalmetal having the same metallurgical characteristics and work historysuch that said member and gas pipe exhibit substantially uniform ther--mal expansion and stress relieving; and

said flange portion and confronting edges being continuously weldedalong the length thereof, said flange portion serving as a source ofWelding metal to provide a mechanically strong large area weld in theregion of said predetermined beveled configuration and along the lengthof said muie structure.

5. A method of fabricating a unitary elongated furnace muifle comprisingthe steps of:

forming a iirst and a second elongated section of generally U-shapedcross-section from a metal having predetermined metallurgicalcharacteristics and Work history;

forming first and second rectangular sheets of a metal having the samecharacteristics and work history as said elongated sections intorespective pipes each having a tubular portion and a flange portion;

forming a bevel on the outer elongated edges of said 'first yand secondsections;

placing the flange portion of each of said pipes between and in contactwith said beveled elongated edges ,with said flange portion disposed inthe V-shaped groove defined by said beveled edges; and

heating said flange portions and adjacent portions of said confrontingsections to cause formation of a large area mechanically strong weldusing the metal of said flange portion as a source of Welding metal.

References Cited UNITED STATES PATENTS 3,410,544 l1/1968 Beck 263-41JOHiN I. CAMBY, Primary Examiner U .S. Cl. X.R. 29-483 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,615, O82 DatedOctober 26+ 1971 Invencor(s) Jacob Howard Beck It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 49, "tice" should be tive Column 4, line 35, after "gas"insert pipe.

Column 5, line 20 (claim 2), "found" should be -formed Signed and sealedthis 29th day of February 1972.

(SEAL) Attest:

ROBERT GOTTSGHALR EDNAHD I-LFLETCIIEII, JH.

Commissioner' of' Patents Atbestnn; Officer* RM P04050 (1059) uscoMM-Dcsoave-p59 fr U S GOVENMENY PRINTING OFFICE |969 U-365-33l

